As scanning lines conversion techniques for converting picture signals of interlaced scanning into picture signals of progressive scanning, motion adaptive scanning lines interpolation processing is used. In the motion adaptive scanning lines interpolation processing, the motion of pictures by picture signals is detected, to produce interpolation scanning lines by inter-field interpolation using picture signals in the preceding field in the case of still pictures, while producing interpolation scanning lines by inter-field interpolation using picture signals in the same field in the case of moving pictures.
FIG. 14 is a schematic view for explaining conventional scanning lines interpolation processing. In FIG. 14, the vertical axis indicates the vertical direction of a picture, and the horizontal axis indicates time.
FIG. 15 is a diagram showing a picture motion judgment method. In FIG. 15, the vertical axis indicates an inter-frame difference, and the horizontal axis indicates the size of an inter-field vertical edge.
In FIG. 14, A0, A2, and A4 respectively represent pixels in a picture in the (n−1)-field, B1 and B3 respectively represent pixels in a picture in the n-th field, and C0, C2, and C4 respectively represent pixels in a picture in the (n+1)-th field. IN represents a picture to be interpolated (hereinafter referred to as an interpolation pixel).
In a conventional motion judgment method, the difference between pixels in the same coordinates in continuous two frames (an inter-frame difference) and the absolute value of the difference between two pixels which are arranged in the vertical direction in the same field (a vertical edge) are calculated as motion information, to judge whether a picture moves or stands still by a combination of the value of the inter-frame difference and the value of the vertical edge, as shown in FIG. 15.
As the inter-frame difference, the absolute value of the difference between the value of the pixel A2 and the value of the pixel C2, for example, is calculated. As the value of the vertical edge, the difference between the value of the pixel B1 and the value of the pixel B3, for example, is calculated.
When the value of the inter-frame difference is large, and the value of the vertical edge is small, it is judged that the motion of the picture is large (the picture is a moving picture). When the value of the inter-frame difference is small, and the value of the vertical edge is large, it is judged that the motion of the picture is small (the picture is a still picture).
In the above-mentioned conventional motion judgment method, however, the motion and the stillness of the picture, as shown in FIGS. 16 and 17, cannot be accurately judged.
FIG. 16(a) is a schematic view illustrating a vertically striped picture which moves in the horizontal direction, and FIGS. 16(b), 16(c), and 16(d) respectively illustrate a picture in the (n−1)-th field, a picture in the n-th field, and a picture in the (n+1)-th field in a case where the picture shown in FIG. 16(a) is expressed by a interlaced scanning system.
FIG. 17(a) is a schematic view illustrating a horizontally striped picture which stands still, and FIGS. 17(b), 17(c), and 17(d) respectively illustrate a picture in the (n−1)-th field, a picture in the n-th field, and a picture in the (n+1)-th field in a case where the picture shown in FIG. 17(a) is expressed by a interlaced scanning system.
As shown in FIG. 16, in the vertically striped picture which moves in the horizontal direction, the value of the inter-frame difference (C2−A2) is zero, and the value of the vertical edge (B1−B3) is also zero.
As shown in FIG. 17, also in the horizontally striped picture which stands still, the value of the inter-frame difference (C2−A2) is zero, and the value of the vertical edge (B1−B3) is also zero.
In the conventional picture motion judgment method, the vertically striped picture which moves in the horizontal direction and the horizontally striped picture which stands still cannot be thus distinguished.
In JP-A-8-54087, an interpolation method for performing scanning lines interpolation processing without judging the motion of a picture has been proposed. In this method, an intermediate value out of a value calculated using pixels above or below an interpolation pixel in the current field, the value of a pixel in the preceding field in the same coordinates as those of the interpolation pixel, and the value of a pixel in the succeeding field in the same coordinates as those of the interpolation pixel is selected as the value of the interpolation pixel. Consequently, a scanning line can be interpolated without judging a still picture and a moving picture.
According to the above-mentioned interpolation method in which the intermediate value is selected, however, the interpolation pixel which should be black and the interpolation pixel which should be white in the striped picture which completely stands still, for example, may, in some case, be gray. Therefore, it is not desirable that the interpolation method in which the intermediate value is selected is applied to the picture which completely stands still. Consequently, it is necessary to accurately judge whether or not the picture stands still.
An object of the present invention is to provide a stillness judgment apparatus capable of accurately judging whether or not a picture stands still and a scanning lines interpolation apparatus using the same.